It's easy to call Facebook the social network of the past. It's harder to build the social network of the future.

To hear Bradley Horowitz tell it, though, Google is well on its way. Google+, he says, lets people share with others in a more natural way than its competitors. Easy privacy controls, an environment free from obtrusive advertising, and highly polished mobile apps combine on Google+ to deliver a next-generation social network, as Horowitz tells it.

The 15-minute interview with Google's vice president of product for Google+ showed off a refreshingly pugnacious side of a social network that's been rather quiet as of late -- and, in doing so, got the network its best press coverage in months. (Slagging on Facebook's increasingly advertising-heavy newsfeed, which no one besides Facebook investors are excited about, can do that for you.) Horowitz went on to suggest that Facebook fails to capture the way people interact in the real world. As a result, he drew renewed attention to the Facebook-Google rivalry that began in earnest last year when Google, a laggard in social software, launched Google+.

But the fascination with Google+ as a would-be Facebook killer obscures the larger story about what Google+ offers. Yes, Google+ competes with Facebook -- for users, for buzz, and ultimately, for ad dollars. But it means more to Google than simply fending off a fast-growing competitor.

Google+ is really two things. One is a destination for connecting with friends and subjects that interest them. When the press writes about Google+, it's usually in this context.

But Google+ plays a second role, as a product that improves other products. Google tends to talk about this in abstract terms -- it's "a social spine;" it's a "fabric;" it "weaves" Google products together. Let's try to be a little more concrete about what Google+ is doing besides giving people a Facebook alternative.

Google+ is a feed of what your friends share online. Did your friend download an app in the Google Play store? Her name will show up front and center when you search for the same app. Searching Google Shopping? Your friends' reviews rise to the top. Did your friend click +1 on a link they found through search? You'll see it when you run your own query on the same subject. Google calls these "social signals," and views them as an essential part of improving nearly all their consumer products. Expect to see more of them.

Google+ is a single sign-on system. Until the social network launched in June 2011, users of various Google services used different identities for each. You were one person on Gmail, another on YouTube, yet another on Blogger. When you visited the search engine, you were little more than an IP address. This drove Google crazy. (It wasn't much fun for users keeping track of different logins and passwords for each service, either.) By creating a single, unified login, Google gained the ability to personalize services (and ads) across all its products. This has not been universally popular, but it has almost certainly been simpler.

Google+ is a data mine. The unified login means Google can start tracking users' interests and behavior around the Web. Follow a bunch of ski resorts on Google+, and Google might eventually show you more search ads for skiing products. If your friends like a certain brand, that might show up higher in results, along with a "social annotation" informing you of your friend's endorsement. Advertisers are arguably way more interested in this stuff than users are, but Google contends that it leads to more relevant ads from which everyone benefits. (So far, companies have found that those social annotations boost ad clicks by double-digit percentages, Google says.)

"Over the past decade, Google has come to provide the products and services that have become essential to internet users... not only Google search but also the Chrome browser, the Android phone, YouTube, Gmail... the list goes on and on," Horowitz told me in an e-mail. "Google+ was designed from its inception as a foundational, unifying layer that makes these already great services even greater. So Google+ is different. It's not only an innovative new social network, it is also the identity, relationship and interest system for Google."

What's important about these aspects of Google+ is that they benefit the company and its customers regardless of whether Google+ ultimately wipes Facebook off the map. The social signals, personalization and improved ad targeting that Google+ creates are arguably by themselves enough to justify the entire effort from Google's perspective. It may be less compelling as a news story than a virtual death match between Mark Zuckerberg and Larry Page, but it's real.

But don't underestimate FacebookThat said, Horowitz did say Facebook is the social network of the past. And for now that looks like a case of Google spin getting ahead of the facts.

Facebook's billion monthly active users make it 10 times the size of Google+, even if Google did hit the 100 million active-user mark in roughly a quarter of the time that Facebook did. Zuckerberg and Co. have made Facebook indispensable across a wide range of products. Its photos, events and messaging features are world class. Timeline has successfully enticed millions of people to upload their entire lives to the service, turning it into a virtual scrapbook that would be hard to abandon. Facebook Connect has become a wildly popular, near-universal login for countless apps and much of the Web. (The company says eight of the top 10 iOS apps, and 40 percent of the top 400 apps, integrate with Facebook.) Then there's the Open Graph, still in its early stages, which aspires to bring the rest of the Web directly into the news feed.

To this high-stakes fight over the future of social networking, Google+ has brought ... privacy controls. And video chat. And a promise to keep ads out of the news feed, at least for now. Plus some nice mobile apps.

It's little wonder, then, that according to (admittedly ancient) available statistics on the average amount of time users spend in each social network, Facebook is ahead of Google+ by leaps and bounds. Google said in June that active users spend 12 minutes a day on the site; we requested updated numbers from ComScore, which furnished numbers to the Wall Street Journal in February on the subject, and didn't hear back.

Of course, Facebook took longer than the 18 months that Google+ has been in the marketplace to become the juggernaut it is today. And it's easy to forget that people thought Google was hopelessly late to the party when it launched ... a search engine.

To date, Google has focused on using Google+ to improve its existing products. The bigger test of the network will come when it invests more heavily in turning it into a destination, giving users a reason to return to it constantly. Horowitz said he aspires to make Google+ the social network where you go to wish your friends a happy birthday. That's a long way off.

Even if Google+ never becomes the Web's hottest property, Google still stands to reap significant benefits from it. Facebook doesn't have to lose for Google+ to be successful. But Google will invest huge resources into seeing that it does. As Horowitz showed this week, Google is coming out swinging. Now let's see if it can land a punch.